The long term goal of this research project is an understanding of the molecule mechanisms of genetic recombination in yeast. In the experiments presented in this proposal, we will isolate and characterize yeast DNA sequences which act as preferred sites for the initiation of recombination events. In addition, we will examine the recombination of yeast transposable elements and the interaction of these sequences with a repressor of recombination. Genetic recombination events are not uniformly distributed along the chromosome; instead, there exist special sites (hotspots) which act as localized stimulators of genetic exchange. It is our goal to isolate yeast recombination hotspots and to examine their mechanism of action. We have already shown that DNA sequence present in the ribosomal RNA gene cluster contains a recombination hotspot. The specific aims of the experiments presented in this proposal are: (1) to examine the mechanism of action of the hotspot present in ribosomal DNA, (2) to isolate additional sequences which act as recombination hotspots and (3) to isolate mutations in the genes whose products initiate recombination events at hotspots. Yeast Ty (transposon yeast) elements can be excised from the yeast genome by recombination between the terminally repeated Delta sequences present at their ends. The SPM2 gene product inhibits the excision of at least one transposon, known as Ty912. In order to examine the mechanism of action of the SPM2 gene product, we will determine its effect on Ty912 transcription, on chromatin structure in an around Ty912 and on the excision of Ty elements other than Ty912. Several lines of evidence suggest that the Delta sequences are the preferred sites of recombination between Ty elements. To examine the role of the Delta's in Ty recombination, we will examine recombination between Ty elements which lack Delta's.